1. Field of the Invention
The present invention relates to electrical systems having dual-voltage control for an electrical load.
2. Description of the Related Art
A feature which is increasingly provided on motor vehicles is daytime running lamps (DRL). In a vehicle with DRL, the headlamps of the vehicle are normally illuminated when the vehicle's engine is running. This illumination is generally with reduced brightness with respect to the full brightness of the headlamps.
In a DRL system, manually turning on the vehicle's headlamps will override the DRL system and provide full-brightness illumination of the headlamps. Further, a manual override function is frequently provided such that the vehicle can be idled without the DRL system turning on the headlamps. This manual override function is sometimes provided by the driver of the vehicle setting the vehicle's parking brake.
A challenge in the design of DRL systems is providing the reduced illumination intensity of the headlamps. A number of ways to do this have been proposed. In one, a dropping resistor is selectively inserted into the headlamp feed circuit when DRL illuminates the headlamps. This dropping resistor provides the reduced-brightness illumination of the headlamps which is characteristic of DRL systems. In another DRL configuration, an electronic module pulse-width-modulates power supplied for illumination of the headlamps. When the headlamps are illuminated in DRL mode, the module provides a voltage of reduced duty cycle. The headlamps thus are illuminated with reduced brightness. In yet another DRL configuration, the headlamps are switchably connected in series when illuminated in DRL mode. This series connection, as opposed to the normal parallel connection of the headlamps, provides reduced illumination intensity of the headlamps.
Each of the proposed designs detailed above, although effective in providing a DRL function, has shortcomings. The dropping resistor design can waste a substantial amount of electrical energy. Further, the pulse-width-modulation design and the headlamps-in-series design are expensive designs, each having an electronic module for controlling the DRL function.
Therefore, a daytime running lamp system which is cost-effective and relatively energy-efficient will provide advantages over the prior art.